diff --git a/src/Facility.CodeGen.JavaScript/JavaScriptGenerator.cs b/src/Facility.CodeGen.JavaScript/JavaScriptGenerator.cs
index 5c7e023..9eaf4df 100644
--- a/src/Facility.CodeGen.JavaScript/JavaScriptGenerator.cs
+++ b/src/Facility.CodeGen.JavaScript/JavaScriptGenerator.cs
@@ -46,6 +46,11 @@ public static int GenerateJavaScript(JavaScriptGeneratorSettings settings) =>
 		/// </summary>
 		public bool DisableESLint { get; set; }
 
+		/// <summary>
+		/// Suffix to append to generated file names before the extension.
+		/// </summary>
+		public string? FileNameSuffix { get; set; }
+
 		/// <summary>
 		/// Generates the JavaScript/TypeScript output.
 		/// </summary>
@@ -58,9 +63,9 @@ public override CodeGenOutput GenerateOutput(ServiceInfo service)
 
 			var moduleName = ModuleName ?? service.Name;
 			var capModuleName = CodeGenUtility.Capitalize(moduleName);
-			var typesFileName = CodeGenUtility.Uncapitalize(moduleName) + "Types" + (TypeScript ? ".ts" : ".js");
-			var clientFileName = CodeGenUtility.Uncapitalize(moduleName) + (TypeScript ? ".ts" : ".js");
-			var serverFileName = CodeGenUtility.Uncapitalize(moduleName) + "Server" + (TypeScript ? ".ts" : ".js");
+			var typesFileName = CodeGenUtility.Uncapitalize(moduleName) + "Types" + (FileNameSuffix ?? "") + (TypeScript ? ".ts" : ".js");
+			var clientFileName = CodeGenUtility.Uncapitalize(moduleName) + (FileNameSuffix ?? "") + (TypeScript ? ".ts" : ".js");
+			var serverFileName = CodeGenUtility.Uncapitalize(moduleName) + "Server" + (FileNameSuffix ?? "") + (TypeScript ? ".ts" : ".js");
 
 			var errors = new List<ServiceDefinitionError>();
 			var namedTexts = new List<CodeGenFile>();
@@ -529,6 +534,7 @@ public override void ApplySettings(FileGeneratorSettings settings)
 			Express = ourSettings.Express;
 			Fastify = ourSettings.Fastify;
 			DisableESLint = ourSettings.DisableESLint;
+			FileNameSuffix = ourSettings.FileNameSuffix;
 		}
 
 		/// <summary>
diff --git a/src/Facility.CodeGen.JavaScript/JavaScriptGeneratorSettings.cs b/src/Facility.CodeGen.JavaScript/JavaScriptGeneratorSettings.cs
index dbf0b2e..6261b86 100644
--- a/src/Facility.CodeGen.JavaScript/JavaScriptGeneratorSettings.cs
+++ b/src/Facility.CodeGen.JavaScript/JavaScriptGeneratorSettings.cs
@@ -34,5 +34,10 @@ public sealed class JavaScriptGeneratorSettings : FileGeneratorSettings
 		/// True to disable ESLint via code comment.
 		/// </summary>
 		public bool DisableESLint { get; set; }
+
+		/// <summary>
+		/// Suffix to append to generated file names before the extension.
+		/// </summary>
+		public string? FileNameSuffix { get; set; }
 	}
 }
diff --git a/src/fsdgenjs/FsdGenJavaScriptApp.cs b/src/fsdgenjs/FsdGenJavaScriptApp.cs
index 7be9d4e..06759cc 100644
--- a/src/fsdgenjs/FsdGenJavaScriptApp.cs
+++ b/src/fsdgenjs/FsdGenJavaScriptApp.cs
@@ -26,6 +26,8 @@ public sealed class FsdGenJavaScriptApp : CodeGeneratorApp
 			"      Generates a Fastify plugin. When specified, only the server plugin is generated, not the client.",
 			"   --disable-eslint",
 			"      Disables ESLint via code comment.",
+			"   --file-name-suffix",
+			"      Suffix to append to generated file names before the file extension.",
 		];
 
 		protected override CodeGenerator CreateGenerator() => new JavaScriptGenerator();
@@ -38,6 +40,7 @@ protected override FileGeneratorSettings CreateSettings(ArgsReader args) =>
 				Express = args.ReadFlag("express"),
 				Fastify = args.ReadFlag("fastify"),
 				DisableESLint = args.ReadFlag("disable-eslint"),
+				FileNameSuffix = args.ReadOption("file-name-suffix"),
 			};
 	}
 }
diff --git a/tests/Facility.CodeGen.JavaScript.UnitTests/JavaScriptGeneratorTests.cs b/tests/Facility.CodeGen.JavaScript.UnitTests/JavaScriptGeneratorTests.cs
index 85a1753..18ca755 100644
--- a/tests/Facility.CodeGen.JavaScript.UnitTests/JavaScriptGeneratorTests.cs
+++ b/tests/Facility.CodeGen.JavaScript.UnitTests/JavaScriptGeneratorTests.cs
@@ -1,5 +1,6 @@
 using System.Reflection;
 using Facility.Definition;
+using Facility.Definition.CodeGen;
 using Facility.Definition.Fsd;
 using FluentAssertions;
 using NUnit.Framework;
@@ -277,6 +278,31 @@ export enum ExampleApiErrors {
 			Assert.That(typesFile.Text, Contains.Substring(expectedErrorSet));
 		}
 
+		[TestCase("", true)]
+		[TestCase("", false)]
+		[TestCase("suffix", true)]
+		[TestCase("suffix", false)]
+		[TestCase(".g", true)]
+		[TestCase(".g", false)]
+		public void GenerateWithCustomFileNameSuffix(string suffix, bool isTypeScript)
+		{
+			const string definition = "service TestApi { }";
+			var parser = new FsdParser();
+			var service = parser.ParseDefinition(new ServiceDefinitionText("TestApi.fsd", definition));
+			var generator = new JavaScriptGenerator { GeneratorName = "JavaScriptGeneratorTests", TypeScript = isTypeScript, Express = true, FileNameSuffix = suffix };
+			var result = generator.GenerateOutput(service);
+			Assert.That(result, Is.Not.Null);
+
+			Assert.That(result.Files, Has.Count.EqualTo(isTypeScript ? 3 : 2));
+			var fullSuffix = suffix + (isTypeScript ? ".ts" : ".js");
+			Assert.That(result.Files, Has.One.Matches<CodeGenFile>(f => f.Name == $"testApi{fullSuffix}"));
+			Assert.That(result.Files, Has.One.Matches<CodeGenFile>(f => f.Name == $"testApi{fullSuffix}"));
+			Assert.That(result.Files, Has.One.Matches<CodeGenFile>(f => f.Name == $"testApiServer{fullSuffix}"));
+
+			if (isTypeScript)
+				Assert.That(result.Files.SingleOrDefault(f => f.Name == $"testApiTypes{fullSuffix}"), Is.Not.Null);
+		}
+
 		private void ThrowsServiceDefinitionException(string definition, string message)
 		{
 			var parser = new FsdParser();